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The wet insulation in the unit is adding to your humidity problem. Need to get a tech to remedy the problem. Also need more return, what you have is not sufficient for 3 tons at a reasonable static. If you increase the area of return the air will have more time to contact the cold coil and remove more water from the air.

Also need more return, what you have is not sufficient for 3 tons at a reasonable static. If you increase the area of return the air will have more time to contact the cold coil and remove more water from the air.

Larger ducts/returns reduces static pressure which increases the total cfm flowing through the coil. With more air flow through the coil, the coil is warmer and removes less moisture and more sensible. Please explain how more moisture is removed by increasing area of return. This not correct advice.
Less restriction requires lower blower speed to get 45-48^F coil temp.
Regards TB

Please explain how more moisture is removed by increasing area of return. This not correct advice.

The blower has already been lowered to its lowest setting on the APH15 HP. This has helped just a little, but now the air from the supply lines moves so slowly there are spots in the house where the air does not get stirred up enough for comfort. This includes the master bathroom which is also a source of humidity inside.

The idea is that we can get more air to the system and not have to slow the fan speed down so low to get the proper dehumidifcation. Also, there is condensation that has been blowing off the coils onto the bottom of the unit on the blower side of the coil.

Please let me know if there are other ways to attack this problem. 6 tons for 3200 sq feet is definitely oversized, but the upstairs unit runs only its #1 compressor most times and that keeps the RH upstairs very comfortable. I may duct kit my Santa Fe Advance, but I'd like the heat pump to be running as close to spec as possible before I try other options.

The blower has already been lowered to its lowest setting on the APH15 HP. This has helped just a little, but now the air from the supply lines moves so slowly there are spots in the house where the air does not get stirred up enough for comfort. This includes the master bathroom which is also a source of humidity inside.

The idea is that we can get more air to the system and not have to slow the fan speed down so low to get the proper dehumidifcation. Also, there is condensation that has been blowing off the coils onto the bottom of the unit on the blower side of the coil.

Seems a big jump to that conclusion, and it may be taking you in the wrong direction. You sure temp imbalance is not more due to cycle time being so short?

I don't think you want to speed air across your coil unless it's freezing up.

"maybe we need to sir up the air more..."? This is feeling a bit like throwing money at everything but the root of problem, hoping for a successful outcome.

Seems the two best options are downsize the equipment, or dehumidify the whole house.

back on page one you wrote:
5) Upstairs has no return duct, just a box - unit is in a closet right beside the grille.
is this closet open to attic at top of closet or closed in & sealed around plenum?

platform that unit sets on should be caulked to walls of closet to seperate
top of closet from r/a below.
inside of r/a should be sheetrocked, or sealed with ductboard. open to studs allows more
leakage. 2x's at bottom of r/a should be caulked to floor of r/a.
door of closet should seal tightly to platform equipment sits upon.
I generally use a piece of armaflex to make this seal.

other r/a are in ceilings or low on walls with chase to r/a in attic?

I'm not clear on where you are adding r/a.
is it upstairs? if so..is there a wall of the r/a that could be used
to add r/a grill? if unit is in closet..door of closet has r/a grill
right?

this may not be the fix..but it wll contribute to high RH if not
sealed air tight.

best of luck.

Last edited by energy_rater_La; 10-06-2012 at 06:21 PM.
Reason: sp

The cure of the part should not be attempted without the cure of the whole. ~Plato

RH issues are all downstairs with the Amana package HP

The upstairs system sits on top of a plywood return box in the closet. RH upstairs stays below 60% year round. It's an Am Std 20 SEER and seems to work great.

Downstairs is the big issue. I have one noisy 25x25 return grille in the hall w/ a 16" round flex going to the unit. We are adding a 14x25 return grille in the foyer in a closet below the stairs. They will use plywood (unless I request otherwise). A 12" flex duct will go from there to a mixing box just inside the crawlspace a few feet from the package unit. The mixing box will take the 16" flex and 12" flex in and have a 18" flex going out to the unit. The 18" flex run will be quite short, maybe 5 or 6 feet. The tech says we will need to reduce the 18" down to 16" right at the package unit with an Amana adapter. The original installer did not use Amana Square to Round adapters, the 20" square to 16" round adapter they installed is too large and disrupting the air flow.

Larger ducts/returns reduces static pressure which increases the total cfm flowing through the coil. With more air flow through the coil, the coil is warmer and removes less moisture and more sensible. Please explain how more moisture is removed by increasing area of return. This not correct advice.
Less restriction requires lower blower speed to get 45-48^F coil temp.
Regards TB

The upstairs system sits on top of a plywood return box in the closet. RH upstairs stays below 60% year round. It's an Am Std 20 SEER and seems to work great.

Downstairs is the big issue.

Because downstairs is the issue means the downstairs system is the problem?

Ever hear "correlation does not prove causation"? be careful of big conclusion jumps.

If upstairs has poor return, and rooms are pressurized, air is being forced out every crack or crevice. If your upstairs system pushing air out holes, that air is being replaced somewhere. That somewhere may be every crack and crevice downstairs. Hot, sticky air.

So the upstairs system could be the cause/partial cause of downstairs comfort issues. (I think 2 system design approach sucks, but I guess sometimes it blows.)

I have talked to two technicians and received offsite consultation from a third (not to mention everyone on HVAC Talk whom I really appreciate). Two of the three I spoke with agree that increasing the filter area and return duct size along with adding a return in another part of the first floor living space will reduce the speed of the air entering the package unit and thus slow the air down so as to prevent water from blowing off the coils. I'm no expert by any means, but it seems like less restriction and lower pressure would mean the same volume of air could flow through the system w/o so much velocity? Please keep in mind we've slowed the blower waaaay down and it still doesn't come close to icing up.

For those asking about return leakage, both returns are sealed with mastic and big gaps sealed with great stuff expanding foam.

...to slow the air down so as to prevent water from blowing off the coils. I'm no expert by any means, but it seems like less restriction and lower pressure would mean the same volume of air could flow through the system w/o so much velocity? Please keep in mind we've slowed the blower waaaay down and it still doesn't come close to icing up.

For those asking about return leakage, both returns are sealed with mastic and big gaps sealed with great stuff expanding foam.

Kind regards,
Backpacker

Addressing your point above in bold, you're on the right track. If your existing return air inlet is undersized for your unit, increasing the inlet size will reduce the velocity of the air entering the unit. Will it increase the volume of air entering the unit (which is what you're really after, since effective dehumidification and cooling of a building depends on sufficient turnover of the volume of air contained in the building)? That depends. If your supply ducts are restrictive and poorly installed, any increase in return air size, while netting perhaps a decrease in velocity, may not yet yield sufficient volume.

Why? Imagine this. You have a section of garden hose about four feet long. You stick your mouth over one end and blow air through the hose. You feel air exit the opposite side. You then think "I wonder if I can get more air through the hose if I make the end I'm blowing air into larger?". So you do it. You make a funnel that you can still fit your mouth around, stick it into one end of the hose (without actually reducing the area of that end's opening), and blow into it. You then find it's just as hard to blow into the hose as before, and you don't get any more air out of it than before. You may feel like less air is rushing out of your mouth and into the hose, but all you have done is reduced the speed of the air exiting your lungs and entering the hose, not the volume. The resistance the four feet of hose is still the same. Decrease the resistance by making the hose larger in diameter, and it suddenly becomes easier to move air through it. And you can ditch the funnel.

All that said, if your supply ducts are sized properly (iffy), then increasing the return size by itself may bring you some relief. However, if your system is oversized for the heat load of your house, you will still not be happy with your comfort, I believe.

Electricity makes refrigeration happen.

Refrigeration makes the HVAC psychrometric process happen.

HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.

if your supply ducts are sized properly (iffy), then increasing the return size by itself may bring you some relief. However, if your system is oversized for the heat load of your house, you will still not be happy with your comfort, I believe.

Shophound, thanks for the reply. Is there a way to actually measure the supply side to determine if I have a problem there as well?